The present application claims priority to Japanese Patent Application Number 2007-048843, filed Feb. 28, 2007, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a navigation system, an enlarged intersection image display method used in the system, and a map information generating method. In particular, the present invention relates to a navigation system that displays an enlarged intersection image on a screen when a vehicle traveling along a guiding path reaches an intersection, and generates map information including voice information for informing a driver of a traveling direction at the intersection by voice.
2. Description of the Related Art
Conventional navigation systems detect a vehicle position and read map data at the vehicle position and its surroundings from a map recording medium (for example, a CD-ROM, a DVD disk, or a hard disk) in order to draw a map image on a display screen. The system also draws a vehicle position mark in a predetermined position on the map image. As the vehicle position changes in accordance with the movement of the vehicle, the map screen is scrolled but the vehicle position mark is fixed at a predetermined position on the screen to allow the driver to grasp map information for the vehicle position and its surroundings at a glance anytime. In addition to the functions described above, conventional navigation systems are equipped with a guidance path function that searches for a guiding path from a place of departure to a destination and displays the guiding path on a map screen. Conventional systems also have a function that displays an enlarged intersection image on ½ of the screen to indicate a traveling direction at an intersection. The system also displays an arrow or informs a driver by voice of the correct traveling direction at an intersection when the vehicle approaches the intersection.
An intersection guidance unit of the navigation system draws an enlarged intersection image on the screen to align the approach direction of an intersection with a 12 o'clock direction. The intersection guidance unit also draws an arrow image indicating the approach direction on the enlarged intersection image. Further, the intersection guidance unit fixes a coordinate position for the intersection in a vertical direction on the screen regardless of which direction the vehicle is traveling. However, the intersection guidance unit controls the horizontal coordinate position of the intersection on the screen in accordance with the traveling direction. For example, if the traveling direction of the vehicle at the intersection is a straight direction, a slight right turn direction, or a slight left turn direction, the intersection is displayed at the center of the screen in a horizontal direction. If the traveling direction of the vehicle at the intersection is a right turn direction or a sharp right turn direction, the intersection is displayed on the left side of the screen, as viewed in the horizontal direction. If the traveling direction of the vehicle at the intersection is a left turn direction or a sharp left turn direction, the intersection is displayed on the right side of the screen as viewed in a horizontal direction. The enlarged intersection image helps a driver to grasp traffic flow in areas along the traveling direction.
Further, the intersection guidance unit determines a direction in which the vehicle travels, on the basis of an angular difference between a direction in which the vehicle approaches the intersection and a direction in which the vehicle exits from the intersections and informs the driver of the determined traveling direction.
In a conventional car navigation system the enlarged intersection image display and intersection voice navigation determines an intersection approach direction and an intersection exit direction by utilizing coordinate information contained in digitalized map data (line map). The angular difference between the two directions is then used to determine a traveling direction at the intersection and control the enlarged intersection image display and the intersection voice navigation based on the traveling direction.
A road is represented by nodes and a link connecting the nodes. The link is represented by inserting shape complementary points between the nodes, which are used in broken line approximation. An approach direction for an approach link at an intersection corresponds to a direction connecting the intersection and the shape complementary point of the approach link positioned closest to the intersection.
FIG. 19A shows an example of the digitalized map data containing four links L0 to L3, which includes nodes P0 to P3. The links L0 to L3 are connected to an intersection O. The links L0 to L3 also include shape complementary points P11, P21, and P31, which represent exits along the links L0 to L3 that are located near the intersection O. As shown in FIG. 19B, assuming that the link L1 is an approach link and the link L2 is an exit link, an approach direction corresponds to a direction A that connects the intersection node P0 and the shape complementary point P11 closest to the intersection node P0 of the approach link L1. The exit direction is defined by a direction B connecting the intersection node P0 and the shape complementary point P21 that is closest to the intersection node P0.
An enlarged intersection image is drawn on a screen such that the intersection approach direction A is aligned with a 12 o'clock direction. Thus, as shown in FIG. 20, the image is displayed on a screen SCR with the link L1 not completely aligned with a 12 o'clock direction on the displayed image. Further, the exit angle is the angle θ between the approach direction A and the exit direction B (see FIG. 19B), and the traveling direction at the intersection is considered to be a slight left turn direction or a straight direction. As shown in FIG. 20, the intersection is displayed at the horizontal center of the screen. This display orientation causes the area around the link L2, which is actually desired, to be insufficiently displayed. Additionally, although a driver feels that the traveling direction is a left turn direction, the traveling direction is erroneously announced as a slight left turn direction or a straight direction.
FIGS. 21A and 21B illustrate a conventional intersection guidance method in which an enlarged image of a 600 ft.×600 ft. area surrounding the intersection is displayed on the screen. In FIG. 21A, O represents an intersection, L1 represents an approach link, and L2 represents an exit link. In the case of voice guided navigation, the main points P1 and P11 of the approach link L1 are not aligned with the 12 o'clock direction, as shown in FIG. 21B. In addition, the voice navigation incorrectly says “Proceed straight (straight direction)”, instead of “Keep slight left (slight left turn direction)”.
FIGS. 22A and 22B illustrate an intersection display position within the enlarged intersection image. In general, if the traveling direction is a right turn direction or a sharp right turn direction, the intersection is displayed on the left side of the intersection display, as shown in FIG. 22A. In FIGS. 22A and 22B, A represents the length of the screen in the horizontal direction, and the intersection is displayed in a position of A/6, as measured from the left side of the screen, in order to display the area near the traveling direction in detail. Further, if the traveling direction is a left turn direction or a sharp left turn direction, the intersection is displayed on the right side as viewed in the horizontal direction of the screen as shown in FIG. 22B, for example in a position of A*⅘, as measured from the left side, to display an area in the traveling direction in detail. If the approach link L1 is aligned in the 12 o'clock direction and a direction connecting the intersection O and the shape complementary point P21 is a slight right turn direction, as shown in FIG. 23A, the traveling direction at the intersection O is announced as a slight right turn direction although the driver feels that the traveling direction is a straight direction. This causes a problem in that the intersection is displayed on the left side of the enlarged intersection display, as shown in FIG. 23B. Thus not enough space is shown on the left side of the road, and too much space is shown on the right side of the road.
FIGS. 24A and 24B illustrate a conventional enlarged image display method for consecutive intersections. FIG. 24A shows an enlarged intersection image including intersections O1 and O2, where the distance between intersections O1 and O2 is within a preset distance. In this example, the enlarged intersection image is displayed such that a direction connecting the shape complementary point P11 of the approach link L1 and the intersection O1 is aligned with the 12 o'clock direction. Thus, the traveling direction at the first intersection O1 is a sharp left turn direction, and the traveling direction at the second intersection O2 is a right turn direction. Further, the navigation system says “in about xxx miles, make a sharp left turn then right turn.” However, as shown in FIG. 24B, this voice instruction is not consistent with the driver's perception.
Japanese Unexamined Patent Application Publication No. 11-51685 discloses a conventional technique of calculating angles at multiple sampling points on links of an intersection to determine a link direction in accordance with the calculated angles, and to output direction guidance information on the basis of the determination result.
However, this conventional technique calculates angles at multiple sampling points in order to determine a link direction, which requires complex calculations. Moreover, the conventional technique is not compatible with consecutive intersections.